Thermoplastics are used on a large scale for the manufacture of bottles such as those extensively used to package beverages including carbonated soft drinks, beer, or mineral water. Many bottle manufacturers prefer using colored bottles. Typical bottle colorations include greens, reds, yellows, browns, and mixtures of colors.
During manufacture, if the eventual bottle is to be colored, one or more dyes are typically admixed with thermoplastic granules charged to the hopper of the injection molding machine used to make the bottle preform. For this purpose the colorant or mixture of colorants can be added as a solid concentrate or in powder form or as a dispersion in a liquid carrier. Additives such as UV filters, oxygen absorbers, antimicrobial agents, antioxidants, light stabilizers, optical brighteners, processing stabilizers, or flame retardants, among others may also be added to the thermoplastic molding composition at or around the same time.
Recent processes of providing coloration to a thermoplastic involve infusing a thermoplastic material with a dye in a dye bath such as is found in U.S. Pat. No. 7,175,675, or by spraying a colorant onto the surface of the article as described in U.S. Pat. No. 6,994,735. Upon formation of the final product, the colored layer is stretched to less than 1 millimeter (mm) in depth, but still provides sufficient coloration to provide a desirable packaging for sale to a consumer.
Unfortunately, the use of color in recyclable thermoplastics presents numerous difficulties for future uses. The presence of the dye in the thermoplastic material is difficult to remove so as to allow subsequent use in future applications requiring clear or non-colored recycled material. Many attempts have been made to remove this color. For example, the dyes have been attempted to be removed by washing steps such as a caustic wash, by heating to damage the dye structure, or by exposing the material to an energy source such as ultraviolet (UV) light. To date, these methods have been unable to remove sufficient coloration of the recycled material for it to be useful. For example, the process of U.S. Patent Application Publication No. 2006/0148914 shows some color change, but as is described therein, full color is not removed from the material. Other attempts at removing color resulted in a yellow tint to the material that is non-removable, thus, contaminating any recycled material and limiting its use in only future colored articles.
As such, there is a long felt need for processes of removing color from thermoplastics during recycling such that the output stream is capable of being used for applications requiring color free materials.